Using camouflage for conservation: colour change in juvenile European lobster

Changes in coloration enable animals to refine their camouflage to match different visual backgrounds, responding to spatial and temporal changes in the environment. Such plasticity provides ecological benefits and could be exploited to support conservation or stock enhancement efforts. One application could be to ensure that hatchery-reared animals, reared to stock wild populations, are appropriately matched to their environment on release. Following crashes in wild European lobster (Homarus gammarus) populations, hatcheries were established across Europe to restock or enhance local lobster stocks by rearing juveniles through their most vulnerable stages, then releasing them into the wild. However, little consideration has yet been given to their camouflage and the implications of matching individuals to the appearance of their release site. This study assesses to what extent juvenile lobsters can change appearance to match their background and whether hatchery practices can be altered to enhance lobster camouflage and potentially survivorship in the wild. We test this by switching individuals between black or white backgrounds in the laboratory and monitoring their coloration over time. We show that juvenile lobsters are capable of changes in luminance (perceived lightness) to better match their background over 2–3 weeks. These changes potentially correspond to improved camouflage, based on a model of predator (fish, Pollachius pollachius) vision. Over a longer period (5 weeks), lobsters maintained on either black or white backgrounds converged on the same darker coloration, likely due to ontogenetic (developmental) changes. Overall, our results indicate that hatcheries could rear lobsters on backgrounds that better match the habitat into which they will be released, but such manipulations should be considered in the context of ontogenetic changes and the timing of release. We recommend rearing individuals on darker, more natural-coloured substrates throughout their early benthic phase in order to maximise the benefits of camouflage on release into the wild. This could potentially increase juvenile survival during the critical days immediately after their release. The findings highlight the potential benefits of using camouflage and colour change in stocking programmes and aquaculture alike.


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Background matching is one of the most widely used anti-predator defence strategies in 39 nature (Stevens & Merilaita, 2011), with many species using colours and patterns to match   (Fig. 1), enclosed within a heavy-duty plastic bag containing seawater (32 +/-2 ‰ 128 salinity) and pure oxygen. This was secured within a 50 x 50 x 100 cm cool box to stabilise 129 temperature during transport. Experimental glass tanks were set up to mimic hatchery were topped up with freshwater to compensate for evaporation during the course of the 138 experiment. Tanks were prepared 48 hours before lobster arrival to allow them to reach a 139 stable temperature. 140 Lobsters were housed individually (to prevent harm from aggressive interactions) in 141 containers made from square uPVC gutter pipe (65 mm by 65 mm) cut to 60 mm lengths 142 and covered with a mesh base to allow water through (Fig. S1). All containers were fixed to 143 corner braces and suspended within the tank above waterproof paper corresponding to the 144 experimental treatment (a black or white background). Each juvenile was fed one formulated 145 pellet (1.5 mm diameter -formula undisclosed) daily, in accordance with the NLH feeding 146 regime. Any uneaten food was removed the following day. Tanks were cleaned and half the 147 water was changed twice weekly to limit the build up of bacteria and algae in the tanks. The 148 light regime was set to 12 hours of light and 12 hours of darkness, with lights on from 07:30 149 to 19:30. Where handling was required, lobsters were pipetted between containers using a 150 modified turkey baster, following the approach used by NLH. To determine the capacity of lobsters for background matching, juvenile lobsters were 153 randomly assigned to either a black or a white compartment for a 2.5 or 5-week period.

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Individuals were photographed to determine their initial luminance (lightness as perceived by    Table S1 for model output). After 3 hours of exposure ( Fig. S2), there was no   Table 2.   Despite initially darkening over time (Fig. 2a,b), lobsters showed some plasticity in their  Table 2b.

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The initial darkening observed in both treatments (Fig 2a,b) corresponds to a significant

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Plastic changes in coloration (Fig. 2c,d) corresponded to a small but significant increase in  Table 3 (see Table S2 for mean JNDs).   Table 3.  Table 5.

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Central lines are medians, boxes are interquartile ranges and whiskers are 95% quartiles.

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JNDs are calculated according to pollack vision. Note that a decline in JND corresponds to 357 an increase in camouflage. Model parameters are detailed in Table 5.   individuals became lighter on a white background and darker on a black one over 2-3 weeks 378 (Fig. 2c,d, Fig. 3). This response shows that juvenile European lobsters are capable of some 379 degree of plastic background matching and, over time, have the potential to become 380 increasingly difficult to discern from their surroundings (Fig. 3). However, some of the changes in discriminability are small (less than 1 JND for those on a white background), so is relatively slow, this capacity to adapt will only benefit hatchery-reared juveniles if they are 394 pre-conditioned for the habitat they are released into.

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In both the medium-and long-term experiment, individuals darken initially, with most of that 396 darkening occurring within the first 2.5 weeks (Fig. 2, Fig. 4). Individuals that remained on reach the deeper, darker seabed they will need to be correspondingly dark, so it stands to 414 reason that settlement could act as a trigger for darkening. Long-term darkening is slightly, 415 and temporarily, offset by the plastic response to their background in the medium-term, with 416 those on a white background becoming less dark than those on black (Fig. 4). Understanding the implications of hue as well as brightness on lobster coloration will greatly 465 inform our understanding of phenotypic plasticity in this species, and determine the extent to 466 which rearing environments can be modified to increase the chances of survival in the 467 natural environment. We recommend that hatchery-reared lobsters are reared on 468 backgrounds that match their release site prior to release into the wild, and that precise Data will be archived in the Dryad Digital Repository on publication of this manuscript.